PQBP1 Is a Proximal Sensor of the cGAS-Dependent Innate Response to HIV-1

Abstract

Summary Dendritic cells (DCs) play a critical role in the immune response to viral infection through the facilitation of cell intrinsic antiviral activity and the activation of adaptive immunity. HIV-1 infection of DCs triggers an IRF3-dependent innate immune response, which requires the activity of cyclic GAMP synthase (cGAS). We report the results of a targeted RNAi screen utilizing primary human monocyte-derived DCs (MDDCs) to identify immune regulators that directly interface with HIV-1-encoded features to initiate this innate response. Polyglutamine binding protein 1 (PQBP1) emerged as a strong candidate through this analysis. We found that PQBP1 directly binds to reverse-transcribed HIV-1 DNA and interacts with cGAS to initiate an IRF3-dependent innate response. MDDCs derived from Renpenning Syndrome patients, who harbor mutations in the PQBP1 locus, possess a severely attenuated innate immune response to HIV-1 challenge, underscoring the role of PQBP1 as a proximal innate sensor of a HIV-1 infection.

Sensing of HIV-1 Infection in Tzm-bl Cells with Reconstituted Expression of STING

“…Western blotting revealed robust expression of the cytoplasmic DNA sensors reported to recognize HIV reverse transcription products, IFI16, DDX41 (49), and cGAS (Fig. 1A, Tzm-bl CON), as well as PQBP1, which was recently identified as an adaptor between HIV-1 DNA and cGAS (50). In contrast, expression of STING, an essential adaptor for innate signaling downstream of cGAS (27,51,52), was weak or undetectable on the protein level (Fig.…”

NLRX1 Sequesters STING to Negatively Regulate the Interferon Response, Thereby Facilitating the Replication of HIV-1 and DNA Viruses

“…We next investigated key signaling innate immune pathways upon HIV-1 infection. HIV-1 infection is known to cause phosphorylation of TBK1 and IKKε, which leads to IRF3 activation (Gao et al, 2013; Yoh et al, 2015). The phosphorylation of TBK1, IKKε, and IRF3 was significantly enhanced in THP-1 cells with attenuated NLRX1 expression relative to control cells upon HIV-VSV infection, and this is followed by enhanced STAT1 phosphorylation which is known to be activated by type I IFN (Figure 2F).…”

“…In HIV-1 infected cells, PQBP1/cGAS recognizes HIV-1 DNA and generates cyclic cGAMP to activate STING (Gao et al, 2013; Yoh et al, 2015). To investigate the role of NLRX1 in STING-dependent innate immune signal transduction, we first examined the impact of NLRX1 on STING-induced activation of interferon-stimulated responsive element (ISRE)-luciferase reporter, which is known to be activated by STING, TBK1, and IRF3 (Ishikawa and Barber, 2008; Zhong et al, 2008).…”

“…Recent advances show that HIV-1 complementary DNA but not its genomic RNA induces IRF3 activation and type-I interferon production dependent on cyclic GAMP synthase (cGAS)-STING pathway in human macrophages (Gao et al, 2013). Importantly, the polyglutamine binding protein 1 (PQBP1) is recently identified as the co-receptor of reverse-transcribed HIV-1 DNA and associates with cGAS (Yoh et al, 2015). HIV-1 DNA triggers cGAS to synthesize cyclic GMP-AMP (cGAMP), which is the activator of adaptor protein STING to induce IRF3 and NF-κB activation, thereafter innate immune response (Gao et al, 2013).…”

STING: infection, inflammation and cancer

“…Many DNA viruses have been reported to trigger STING-dependent activity, including adenovirus, vaccinia virus and papilloma virus 2,28–31 .The importance of the cGAS–STING axis has also been demonstrated for retrovirus infection including HIV 32–35 . It is probable that retroviral DNA activates the cGAS–STING axis, although a recent report indicated that retroviral RNA–DNA hybrids can also trigger this pathway suggesting that a wide array of nucleic acid structures may be capable of triggering STING activity 32,33,36–38 .…”